Device for measuring peak currents



June 19, 1945. c.A w.' HANSELL y v DEVICE FOR MEASURING PEAK CURRENTS FiledApil 11, 1942 M M. R M M T p u INVENTOR C24/@Nas W HA/vsELL B* 71%@ ATTORNEY Patented June 19, 1945 2,378,846 e DEVICE FOR. MEASURING PEAK CURRENT Clarence W. Hansell, Rocky Point, N. Y., asslgnor to Radio Corporation of America, a corpora- UNITED STATES PATENT orticay Vinstrument Hfor measuring instantaneous -tlon oi' Delaware Application April 11, 19i2 Serial No.*438`,519`2 ment is performed by impressingV the` potential 4 Claims.

The present invention relates tocurrent measuring instruments and, more particularly, to an peak current intensities.

In rectifier circuits the output ofthe rectifier is limited, to a great extent, by the ability of the rectifier tubes to withstand current peaks occurring each charging cycle for the illter circuit condensers connected thereto. Heretofore known methods of measuring peak current amplitudes,

under such circumstances, involve the use of an p oscilloscope but this has decided disadvantages in most cases since special transformers must be used to insulate the oscilloscope from 'ground because the peak currents must bemeasured in circuits Which are at high potential with respect to ground. The oscilloscope is, of course, then at a high potential withl respect to ground and the problem of focussing the oscilloscope and making other required adjustments is very diilicult. Furthermore, the oscilloscope equipment is bulky and often cannot be placed within the compartment usually provided ina radio transmitter installation for the rectifier equipment.

An object, therefore; of the present invention is the provision of a peak current measuring instrument which does not require specially insulated transformer equipment.

across a rectifier or other unilaterally conductive device and a condenser in.' series, the circuit being sovarranged that the condenser` charges up to substantially the peak potential across the resistance. 'The potential across the condenser may then be measured directly by means of a low `another object of the present invention is theV provision of a. compact peak current instrument which may be placed in thezprotectlon compartment oi' high voltage rectifier equipment.

another object of the present invention is to provide a peak current instrument which may be readily calibrated.

A further object of the present vinvention is the provision ci a peak current measuring instrument which may he calibrated on one range of current intensities and used for other ranges of eurent intensities without recuiring recaiihram tion. Stili e, further object of the present invention is the provision of? means for cambi-ating and checking the apar-ation of peak current instruments..

n The foregoine Gbicctaand others which may appear from the following descriptione are atcurrent, high resistance voltmeter. The resistance of the voltmeter'must be such that only a i very small drop in the condenser potential takes place between pulses of currentfrom therecti- Under such circumstances, the current 11er; takenby the meter causes a negligible error. The

. arrangement may-be calibrated for a potential `rent oif may be varied over a wide range. The

steady 4state current through the circuit maybe measured by aconv'entional direct current am- "meter i1 the commutator is stopped in a closed circuit position. The steady state current, assuming the circuit is substantially purely resis-` tive in nature, is the same as `the peak current value .obtained with the commutator in operation. l

The present vinvention may bemore fullyunderstoodlby reference to the `following detailed description, which is accompanied by a drawing' in which Figure 1 illustratesan embodiment of in the circuit. Then the peak potential drop across the resistance is measured. The measure-` the invention and the manner of employment of the invention for measuring peak current intensities, 'while Figure 2 illustrates a circuit for calibrating the instrument.

In Figure l.Y there-is shown a rectifier circuit including a power transformer 5 having primary and secondary windings t and l, each end of the secondary winding l being connected to an anode of rectier tubes and 9, while a center-tap connection constitutes the negative output lead. The laments of the rectifier `tubes 8 and 9 may be heated from the A. C. power supply through a filamentI transformer l0, as is well known in the art, the positiveoutput' lead being connected to the center tap of the secondary of the lament transformer l0. A variable current limiting reactor II is provided between the rectifier and smoothing condenser I2 to adjust the peak current to the condenser on each charging cycle. The 'direct current outputof the rectifier circuit,

as so farexplained, is limited by the ability of rectier tubes 8 and l9 to withstand the peak condenser I2. If condenser I2 has a fairly high capacity the peak charging pulses may exceed in amplitude by several times th average cur- A rent drawn out of the rectifier circuit.` In order to determine whether or not these peak current pulses exceed the rating of rectiertubes 8 and 9, I propose connecting in series with rst one and then the other of the rectier tubes, a peak current measuring instrument generally indicated by reference numeral yI3. The instrument contains a small tapped `resistor which is connected in series in the rectiiier circuit. The resistance of this resistor I5 must be accurately known, both as to its total value and as to the value with 'switch I6 incontact with the various taps I1, I8, I 9. Across resistor |5`is con'nected a series circuit.A including condenser 20 and rectiier` tube 22.y Rectier tube 22 is so connected that potential peaks developed across resistor I5 'Y cause currentto flow through the rectifier tube 22 to charge condenser 2D. Then, as the peak potential across resistor |5 subsides to a value less than the potential across condenser 20 the rectier 'tube 22'prevents the condenser 20 from being discharged across the resistor.'

While I have shown rectier tube 22 as a thermionic type ofv rectifier having a filament heated by battery 24, it is, of course, within the scope of my invention to utilize dry contact type rectiiiers, if desired.- 1

The'peak potentials developed across Vcondenser 20 are measured by a low current drain voltmeter 25 having a very high internal resistance.

The resistance of vo1tmet5er25 is such that the l current impulses ypassing therethrough to charge v several embodiments of my invention, it is to be Y l 34, thus roughly adjusting the current in the cirthus rotating disc 3|, the speed being adjusted by rheostat 46. The'positicn of brush 34 along va radius of disc 3| is then varied in `order to ob,

tain the desired current on-current off ratio in the circuit. The reading'` of meter 25 in instrument I3 ,is then recorded. The current value in the' circuit may then be changed to a different value and thus Ianentire series of calibrations be determined for meter 25.

While I have shown and particularly described distinctly understood that my invention is not limited thereto but that'modifications within the scope of my invention may be made. I claim:

1. A system for measuring peak current values y in a circuit carrying a fluctuating direct current,

. a series resistor in said circuit, the potential drop across said resistor varying in accordance withy the. instantaneous current values therethrough,

a condenser and a unilaterally conductive device connected in series across said resistor, said device being so poled that said condenser is charged by peak potentials developed across said resistor in response to current flow therethrough, and means for measuring the potential across said condenser, said means having a high internal resistance' whereby the charge on said condenser substantially unaiected thereby.

2. In -a rectifier circuit, a series resistor in said circuit, a condenserand a unilaterally conductive condenserl20 is only slightly discharged by the current drawn by the meter during the time intervalbetween peaks of .current drawn through .resistor I5.

Thus the meter 25 may be calibrated in terms of peak current values in resistor I5 with only negligible error. The scale of the instrument or range of peak current values measured thereby may be readily changed by means'of tap switch I6 selectively contacting taps l1, I8 or I9 on resistor I5. As portions of resistor I5 are successively short-circuited by switch I6 the scale of the instrument is correspondingly multiplied.

. In Figure 2 I have shown a circuit whereby the peak current instrument I3 may be calibrated by comparing its current reading with a standard ammeter 30. The calibration circuit includes a .commutator 3|, the commutator comprising an insulating disc -3I 'carrying a radial conducting strip32 thereon.. 'I'he .contact brush 34'is arranged to swing in an arc over the face of in'l sulating disc 3| from a point near its center to a point near the perimeter. Thus the relationship of the time that. the brush 34 is in contact with .conductive segment 32 with respect to the time that the brush 34 is out oi"v contact with the segment may be adjusted over a wide range. AIn a series arrangementwith vthe commutator 3| are connected the peak current instrument I 3, standard ammeter 30, a battery 36 and a current addevice Vconnected in series across said resistor, said device being so poled that said condenser Ais charged by peak potentials developed acrosssaid resistor in response to current flow therethrough, and means for measuring the potential across said condenser, said means having a high internal resistance whereby the charge on said condenser is substantially unaffected thereby. 3. A system for measuring peak current values in a circuit carrying a fluctuatin'g-direct current,

a series resistor in said circuit, a condenser 'and a'rectiiier connected in series across said-resistor, said rectifier being so poled that said condenser is charged by peak potentials developed' across said resistor inresponse -to current iiow therethrough, and means formeasuring the poten'tial across said condenser, said means having a high internal' resistance whereby the charge on said condenser thereby.

4. In a circuit including a rectifier and a smoothing condenser, a series resistor connected charged by peak potentials developed across said resistor in response to current flow therethrough,

.and means for measuring the potential across said second condenser, said means having a high internal resistance whereby the charge on said secondqcondenser is substantially' unaiected justing rheostat 31. The potential of battery 36 thereby.

CLARENCE HANSlllIL.

is substantially unaiected' 

